1. Field of the Invention
The present invention relates to a method of wet removal of an acidic component in an exhaust gas with seawater, in particular an acidic component exhausted from a boiler or various furnaces, and an acidic component from an exhaust gas containing sulfite gas.
2. Description of the Related Art
At present, for example, when heavy oil, coal, etc. are burned in combustion equipments such as a boiler or various types of furnaces and since the fuels contain a sulfur component, the sulfur component is combined with the oxygen in the air at the time of combustion to form sulfur oxides which end up included in the combustion exhaust gas. Such sulfur oxides travel with the gas from the source of generation to regions as much as several thousand kilometers away to cause phenomena such as acid rain or acid fog, polluting the air, water, soil, etc. over a vast region and having detrimental effects on human health.
However, along with the increased international interest in global environmental issues, global scale measures have been sought. In Japan, along with advances made in exhaust gas desulfurization or denitrogenation technologies etc., efficient boiler combustion technology has been accomplished. Substantially 100% antipolution measures are now taken at the source of generation. For example, as a method of wet removal of the acidic component such as the sulfur oxides contained in the gas, a packed column, spray column, bubble cap column, perforated or grid plate column without weir and downcomer etc. have been used to bring the gas to be treated and an alkali treatment solution countercurrently into contact. That is, it can be said that the desulfurization treatment technology for environmental protection has reached the almost perfected stage. For example, a desulfurization efficiency of 90 to 99% has been obtained and commercialized. However, since calcium hydroxide, calcium carbonate, sodium hydroxide, magnesium hydroxide, etc. are used as the alkali treatment solution, there occur problem that, in addition to higher cost, the waste solutions have to be treated, the solid substances have to be treated, etc. Thus, there are problems of complication of the process and high construction and running costs. Therefore, as a method of treatment of exhaust gas using seawater, the present inventors developed a method of wet treatment of exhaust gas by using a perforated or grid plate column without weir and downcomer in JP-A-11-290643 (method of treatment of acidic component in an exhaust gas with seawater). Nevertheless, this method was insufficient in the low Ug region.
As explained above, even a process for removing an acidic component from an exhaust gas, developments of new technologies for simplification of the process, making the equipment more compact, and sharply reducing the construction and running costs are sought not only in the industrialized countries, but in the developing countries as well. In particular, a reliable process is sought for cases where advanced treatment of all regions, including the low Ug region, is frequently required.
Accordingly, objects of the present invention are to develop new technologies capable of highly removing an acidic component such as a sulfate gas contained in an exhaust gas with a simplified process in a more compact equipment, and at a remarkably reducted the construction and running costs, in view of the international needs, at a wide region including a low Ug and low L/G region.
In accordance with the present invention, there is provided a method for removing an acidic component contained in an exhaust gas comprising by using a system comprising (a) a gas-liquid contact apparatus composed of an absorption column provided internally with at least one perforated plate at the top, bottom, or both top and bottom of the absorption column packed with at least one type of fillers, (b) an apparatus for introducing seawater to the absorption column, (c) an apparatus for oxidizing the seawater after gas-liquid contact, and (d) an apparatus for mixing a noncontact seawater with the seawater after subjected to the mixing and oxidation, whereby the exhaust gas containing an acidic component is brought into gas-liquid contact with the seawater.
In accordance with the present invention, there is also provided a wet method for removing an acidic component contained in an exhaust gas, in a gas-liquid contact apparatus including an absorption column having a column diameter of at least 500 mm and provided with at least one perforated plate having an free-space ratio Fc of 0.25 to 0.5 and provided with at least one type of packing material with a packing height of 0.5 m to 4 m, comprising
supplying seawater in such an amount that a ratio L/G of the flow rate L (kg/m2xc2x7hr) of the seawater to the flow rate G (kg/m2xc2x7hr) of the gas to be treated from the top of the column is at least 3.6 and a flow rate L of the seawater is 1xc3x97104 to 25xc3x97104 kg/m2xc2x7hr and introducing a treated gas in such an amount that a range of a superficial gas velocity Ug in the apparatus from the bottom of the gas-liquid contact apparatus is 0 to 2xc2x7Ugm (m/sec):
in the case of using a perforated or grid plate column without weir and downcomer composed of at least one perforated plate and the ratio xcfx81G/xcfx81L of the density xcfx81G (kg/m3) of the treated gas to the density xcfx81L (kg/m3) of seawater of 1030 is at least 0.838xc3x9710xe2x88x923,
Ugm=49.14 Fc0.7 (xcfx81G/xcfx81Lxc3x9710xe2x88x923)xe2x88x920.5xc2x7(L/G)xe2x88x921/3xc2x7{square root over (gxc2x7L)}
wherein L is a capillary constant {square root over (2"sgr"/xcfx81Lxc2x7g)},
g is a gravitational acceleration (m/sec2) and
"sgr" is a surface tension of seawater (kg/sec2)
whereby the gas to be treated and seawater are countercurrently brought into gas-liquid contact.